1. Field of the Invention
The present invention in general relates to a method and system for improved connection setup procedure while responding for a page (i.e. for mobile terminated calls). More particularly this invention relates to a method and system for efficient connection setup procedure for mobile terminated (MT) calls, with reduced probability of collision during access attempt.
2. Description of the Related Art
Mobile terminated Connection Setup procedure proposed for EVDO evolution system (i.e. 3GPP2 UMB) works [1] in the following manner (as shown in the FIG. 1):
1. Access Network (AN) sends Page message to an Access Terminal (AT), page message contains unique ATI of the paged AT
2. AT selects one access sequence (randomly) and sends access sequence as preamble (with power ramping procedure, if probe is not reaching to AN) Selected access sequence belongs to one of the sets, as all available access sequences are partitioned into sets based on pilot strength level and buffer requirement of the application.
3. AN sends Access Grant (AG) message once access probe is received by it. AG message has the same access sequence sent by AT. AG message may also contain timing information and resources for AT to transmit in the reverse direction. These resources are to be used for exchanging Bind Request/Response messages.
4. AT sends Bind Request (and ConnectionOpenRequest) message to AN. AT sends its unique ATI, and MAC ID (which it has received in AG message).
5. Bind Response is sent by AN to acknowledge Bind request message. Bind Request/Bind Response mechanism ensures that there is no collision during access attempt.
6. AN sends ConnectionOpenResponse message to AT (ConnectionOpenResponse message can be sent as part of Bind Response message or it can be sent as a separate message. This option is provided because MAC ID provided in the AG message expires in 100 ms, and AN may take longer time to find the session related information of AT before AN can send ConnectionOpenResponse message).
Collision During Access Attempt
Collision is a phenomenon when more than one AT uses the same Access Sequence to send their access probe at the same time. AN may detect only one of those access probes. AN will respond with an AG message containing the access sequence corresponding to the detected access probe. But this AG message may be received by more than one AT who have used the same access sequence to send the access probe. Hence all those ATs will treat the AG as a response to their access probe and will go to next step in the connection setup procedure and all of them will claim the MAC ID provided in the AG message. This is the cause of collision during access attempt. To resolve this issue Bind Request/Response mechanism is provided.
Access probe has no payload and it carries only a 10 bit random AccessSequence.
AccessGrant may contains MAC ID, Time offset (for RL OFDM waveform to be within cyclic prefix) and AccessSequence (to distinguish between multiple users who may have sent access probe at the same time).
Access probe and access grant exchange provides to the AT; Dedicated RCC (RL Control Channel) resources (for CQI reporting, REQ channel to request RL OFDM tones), Closed loop power control, Ability for RL/FL unicastdata exchange. From lower layers perspective, connection between sector and AT is established once MAC ID is assigned.
Access probe and Access grant exchange does not provide:                Knowledge of Unique ATI to the sector (Sector does not know session (QoS, security) information),        resolution of access collisions.        